The 1883 eruption of Krakatoa killed roughly 36,000 people. Most of them didn’t die from lava or ash.
They drowned. The volcano—sitting in the Sunda Strait between Java and Sumatra—exploded with such violence that it triggered tsunamis reaching 120 feet high. Entire coastal villages vanished in minutes. Ships were carried miles inland like bathtub toys. And here’s the thing: this wasn’t some freak accident of geology. Volcanoes and tsunamis are partners in catastrophe, locked in a dance that’s been going on for milenia.
Most people imagine volcanoes as mountain-sized fire hoses spewing lava. That’s partially true but wildly incomplete.
When a volcano decides to blow its top underwater—or near enough to the coast—the real danger isn’t always the eruption itself. It’s what happens next. Krakatoa’s 1883 eruption ejected roughly 5 cubic miles of rock into the atmosphere, but the collapse of the volcano’s caldera displaced massive volumes of seawater. Think of it like dropping a boulder into a bathtub, except the bathtub is the Indian Ocean and the boulder weighs several billion tons. The resulting waves radiated outward at speeds exceeding 400 miles per hour, hitting coastlines with apocalyptic force.
Wait—maybe volcanoes don’t even need to explode to cause tsunamis.
When the Mountain Doesn’t Explode But the Ocean Still Goes Berserk
In 1741, Mount Hachijojima in Japan triggered a tsunami without a major eruption. How? A massive landslide. Volcanic mountains are notoriously unstable—they’re essentially piles of loose rock, ash, and hardened lava stacked precariously high. When part of that pile gives way and crashes into the ocean, you get instant tsunami conditions. The 1958 Lituya Bay event in Alaska wasn’t technically volcanic, but it illustrated the principle perfectly: a landslide dropped 90 million tons of rock into the bay, creating a wave that reached 1,720 feet high. That’s taller than the Empire State Building.
Turns out, volcanoes are geological time bombs with multiple detonation mechanisms.
Anak Krakatau—literally “Child of Krakatoa”—demonstrated this in 2018. The volcano had been growing since the 1920s, rebuilding itself from its parent’s catastrophic collapse. On December 22, 2018, a flank collapse sent debris cascading into the Sunda Strait, generating a tsunami that killed over 400 people. No major eruption. Just gravity and bad timing. Coastal communities had no warning because monitoring systems were focused on seismic activity, not structural instability. The wave arrived during a concert on the beach, turning a Saturday night into a tragedy.
Submarine volcanoes add another layer of chaos to this relationship.
The Ones You Can’t See Until the Ocean Starts Behaving Strangely
In January 2022, the Hunga Tonga-Hunga Ha’apai volcano in the South Pacific erupted with such force that it was heard in Alaska—over 6,000 miles away. The explosion generated tsunamis across the Pacific Basin, with waves reaching Japan, Chile, and the U.S. West Coast. Satellite data showed the eruption plume reaching 36 miles into the atmosphere, punching through the stratosphere. The pressure wave circled the globe multiple times. And yet most people had never heard of this volcano before it decided to introduce itself so dramatically.
Submarine eruptions are particularly insidious because they’re difficult to monitor. The ocean hides the visual cues—no ash plume, no glowing lava flows. Just sudden seafloor displacement that sends water surging in all directions. The 1952 eruption of Myojin-sho in Japan sank a research vessel investigating the activity, killing all 31 people aboard. They were trying to study the volcano when it erupted directly beneath them.
Pyroclastic flows—those superheated avalanches of gas, ash, and rock—can also trigger tsunamis when they hit water. Mount Vesuvius demonstrated this in 79 AD, though Pompeii gets all the attention. Recent research suggests that pyroclastic flows from the eruption entered the Bay of Naples, displacing water and creating localized tsunamis. The combination of flows, earthquakes, and possible caldera collapse made the disaster multifaceted.
The geological record shows this pattern repeating across millennia. The Santorini eruption around 1600 BCE—which may have inspired the Atlantis legend—generated tsunamis that devastated Minoan civilization on Crete. Deposits of volcanic ash mixed with marine sediments tell the story of waves carrying ocean debris miles inland. The eruption was roughly four times more powerful than Krakatoa, ejecting an estimated 14 cubic miles of material.
Climate records captured in ice cores and tree rings show the global impact of such eruptions. The 1815 eruption of Mount Tambora in Indonesia—the largest in recorded history—caused the “Year Without a Summer” in 1816. Crop failures, famines, and social upheaval followed. While tsunamis were a local concern during the eruption itself, the global consequences rippled outward through interconnected systems: atmosphere, ocean, agriculture, economy.
Modern monitoring systems try to anticipate these disasters through seismic networks, GPS deformation measurements, and ocean buoys. The Pacific Tsunami Warning Center tracks volcanic activity alongside earthquakes. But predicting exactly when a volcano will collapse, explode, or slide into the ocean remains frustratingly imprecise. Anak Krakatau was being monitored when it collapsed in 2018, yet the tsunami still arrived without adequate warning.
The connection between volcanoes and tsunamis isn’t just about individual events—it’s about understanding how Earth’s systems interact catastrophically. Subduction zones where tectonic plates collide create both volcanic arcs and tsunami-prone fault lines. The Pacific Ring of Fire exemplifies this: a 25,000-mile arc of volcanoes and earthquake zones encircling the Pacific Ocean. Indonesia alone has over 130 active volcanoes and sits astride multiple subduction zones.
We’re living on a planet that regularly rearranges itself with terrifying indifference to human habitation patterns.
